1. Field of the Invention
The present invention relates to an optical switch and an optical network in which the optical switch is used. More particularly, this invention relates to an optical switch having a function in amplifying an input light and an optical network in which the optical switch is used.
2. Description of the Related Art
A photonic switching for performing a path edition with a light intact without converting a light signal into an electric signal in a node can reduce a scale of the node, thus contributing greatly to the reduction of a cost for communication. A switching technique is important in constructing such a node. For example, in an optical ADM (Add/Drop Multiplexing) system, an optical gate switch, by which a signal light is branched or inserted, requires the following properties, i.e., a low crosstalk and a low insertion loss. An EDFA (Erbium-doped Fiber Amplifier) gate switch is exemplified as the switch for satisfying this requirement.
The EDFA gate switch operates as an optical switch by turning on or off a pumping source of EDFA that is an optical fiber amplifier. To switch on the EDFA gate switch, a pumping light is turned on. This permits amplifying and outputting the input light to the EDFA gate switch. On the other hand, to switch off the EDFA gate switch, the pumping light is turned off. This allows the input light to be absorbed into EDF constituting EDFA and thus not to be outputted from EDFA.
With the conventional EDFA gate switch, a single gate switch has fulfilled all of functions as a switch, a controller for an outputted optical power and an optical amplifier. However, a problem exists in that it is difficult for a single gate switch to obtain a high gain and a high power without having an adverse influence on transmission properties.
An object of the present invention is to realize an optical switch which is capable of obtaining a high gain and a high power.
An optical switch of the present invention comprises first and second optical amplifiers connected in cascade; and a first control circuit for outputting first and second control signals for switching a gain of the first and second optical amplifiers.
Another optical switch according to the present invention is an optical switch for a wavelength-division multiplexed light which is obtained by wavelength-division multiplexing a plurality of light signals. The optical switch comprises an optical wavelength demultiplexer, a plurality of single wavelength optical switches, and an optical wavelength multiplexer.
The optical wavelength demultiplexer demultiplexes the wavelength-division multiplexed light into the plurality of light signals and outputs each of the plurality of light signals to each of a plurality of branches. Each of the single wavelength optical switches is connected to each of the plurality of branches. The optical wavelength multiplexer multiplexes the lights outputted from the plurality of single wavelength optical switches. Each of the plurality of single wavelength optical switches comprises and second optical amplifiers connected in cascade, a first optical coupler connected to an input of the first optical amplifier, and a second optical coupler inserted between the first and second optical amplifiers.
An optical switch according to the third aspect of the present invention is also an optical switch for a wavelength-division multiplexed light which is obtained by wavelength-division multiplexing a plurality of light signals. The optical switch comprises an optical wavelength demultiplexer, a plurality of first optical couplers, a plurality of first optical amplifiers, a plurality of second optical couplers, at least one first optical wavelength multiplexer, and at least one second optical amplifier.
The optical wavelength demultiplexer demultiplexes the wavelength-division multiplexed light into the plurality of light signals and outputs each of the plurality of light signals to each of a plurality of branches. Each of the plurality of first optical couplers is connected to each of the plurality of branches. Each of the plurality of first optical amplifiers has an input connected to an output of each of the plurality of first optical couplers. Each of the plurality of second optical couplers has an input-side first branch connected to the output of each of the plurality of first optical amplifiers. Each input of the first optical wavelength multiplexers is connected to each of output-side branches of some of the plurality of second optical couplers. An input of the second optical amplifier is connected to the output of the at least one first optical wavelength multiplexer.
An optical network of the present invention is an optical network in which a plurality of optical nodes are connected through an optical fiber transmission line, wherein each of the plurality of optical nodes comprises an optical switch of the present invention as described above.